Radon is a naturally occurring radioactive gas formed by the decay of radioactive uranium in the ground; it is particularly associated with areas of granite. It is colourless, odourless and tasteless. Geological conditions and the amount of uranium in the ground varies from place to place , as a result radon levels are higher in some parts of the country than in others. Radon normally enters the building through cracks and holes in floors and walls, and gaps around service pipes and cables. It is a heavier than air gas that has a tendency to accumulate in basements and cellars and under suspended floors.

In the open air radon is quickly dispersed and is not a risk to health but when it accumulates in buildings it can be a risk to health particularly when it accumulates in large quantities.

In areas known to be radon hot spots employers must consider the risk to their workforce from exposure to the gas. They may need to arrange for levels to be monitored; where results are above recognised safe limits action must be taken.